Railway cars in a train are connected to an adjacent car by a coupler. The coupler is joined to a yoke and the assembly is mounted in a railway car center sill. In “cushioned” railway cars, to prevent damage to the railway cars and the laded goods during operation, especially during assembly of the railway car train in the yard, various devices have been installed to absorb loads on the coupler so that impact forces transmitted to the railway car are reduced. Generally, either frictional draft gear or hydraulic units are used for this purpose.
In a conventional frictional draft gear, one or more elastic elements, such as a coil spring or a set of elastomeric pads, is enclosed in a housing mounted in the yoke behind the coupler. A piston-like element frictionally received in the housing absorbs buff loads transmitted via a coupler follower which moves inside the yoke in response to buff impact force applied on the coupler, and the draft gear is compressed in the yoke in response to buff and draft forces. The basic draft gear apparatus has been used for decades. However, in many cases unacceptably large forces are transmitted to the railway car and it would be a desirable advance in the art to provide a cushioning apparatus that dissipates more force during impact than the conventional draft gear.
A hydraulic cushioning unit comprises a piston received in a cylinder filled with fluid. Such devices may dissipate more energy than a conventional draft gear, but they are known to be prone to leakage. Further, a hydraulic unit has a response to impact loads characterized by longer travel for the amount of energy dissipated, which can negatively impact train handling. Also, the fluid in a conventional hydraulic unit does not cushion draft forces on the coupler.
U.S. Patent Application Publication No. 2017/0210398 is incorporated by reference herein for its teaching of draft gear functioning and measurement of energy absorption.
U.S. Pat. No. 5,487,480 is incorporated by reference herein for its description of a hydraulic end-of-car cushioning (EOCC) unit.